Help - kitchen ceiling & escape of water

Help! I've had an escape of water. Is there a quick fix or does this all have to come down and new plasterboard go on? It will be a first time for me to do this, so it will be interesting if so...

It's been like this some time so it's as dry and it's going to get.

I'm concerned about damage to the joists. What should I be looking out for if/when I take the ceiling down?

What about the wall? I've never done plastering and not likely to start now. Can this be painted over? It may be best to get someone in if it needs replastering.

 

Has anyone had any experience using damp seal like this:
https://www.screwfix.com/p/thompsons-one-coat-damp-seal-white-2-5ltr/43531

Any recommendations would be much appreciated.
Stu

 

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